Conventionally, a signal transmission device (data interface) mainly uses a transmission system for transmitting a single-ended signal in parallel. However, in accordance with recent demands for increase in speed of the system, the transmission system in the signal transmission device is being replaced by a system for transmitting a differential signal serially.
In such a transit period of the replacement of the transmission system, it is beneficial that a general-purpose signal transmission device dealing with both systems of the conventional transmission system (the transmission system for transmitting the single-ended signal in parallel) and the transmission system to be newly introduced (the transmission system for transmitting differential signal serially), to thereby have compatibility with a device that supports the conventional signal transmission system only.
Different noise countermeasures in the signal transmission device are helpful between the case using the single-ended signal and the case using the differential signal. For example, in the signal transmission device using single-ended signals, a resistor or an inductor for suppressing a normal mode current (differential mode current) is normally used as the noise countermeasure. On the contrary, in the signal transmission device using differential signals, a common mode filter for suppressing a common mode current is normally used as the noise countermeasure.
For this reason, in the signal transmission device which deals with both the transmission system using single-ended signals and the transmission system using differential signals, it is beneficial to take a noise countermeasure suitable for the both systems.
Patent Literature 1 (JP 2009-290843 A) discloses a signal transmission device that deals with both of the signal transmission using differential signals and the signal transmission using single-ended signals. The signal transmission device transmits a differential signal and in-phase single-ended signals to connected two signal lines in a superimposed manner.